Friction-reducing devices called bearings are available in a wide variety of types and are used in machines of virtually all sizes and complexities. A well-known type uses component parts which roll relative to other parts. For example, bicycle hubs use ball bearings, with or without a bearing "race." And every electrically powered home appliance uses one or more bearings. To enlarge the scale of the examples, railroad freight car wheels are supported on tapered roller bearings. Bearings of the foregoing types incorporate a multiplicity of rolling components such as spherical balls, solid cylindrical rollers, slender cylindrical needles or solid tapered rollers.
Such bearings share certain common features. One is that they operate at relatively high speed. Another is that they are known as "hydrodynamically" lubricated bearings in that their operating speed helps assure that critical surfaces are continually coated with a film of lubricant.
However, bearings having rolling components are by no means the only type of bearing used. Another major bearing type is known as a "bushing" or bushing-type bearing, sometimes called a plain journal bearing. In simplest form, bushing-type bearings are hollow cylinders supporting a component such as a shaft. Bearings of the bushing type involve sliding rather than rolling motion and are typically used where relative bearing-component rotation is at a rather slow speed.
Bearings of this type are known as "boundary" lubricated bearings in that there may not be a film of lubricant between the bearing and the adjacent component. Because such bearings support significant loads (for their size) and because, often, the bearing is called upon to function only occasionally, e.g., once or twice a day, lubricant is simply squeezed out from between the relatively moving surfaces.
With larger machines, bearing lubrication--especially in plain journal or bushing bearings--can be a difficult design problem. Nowhere is this more true than in large mobile machines such as earth-moving and earth-excavating machinery.
Such machinery is available in a wide variety of types ranging from the familiar rubber-tire mounted and crawler-mounted to the less-common dragline. A dragline is often used for removing top soil and "overburden" to expose a valuable mineral, e.g., coal, beneath but near the earth's surface.
A dragline is equipped with an angularly-extending boom from which is suspended a "bucket" having an open mouth and digging teeth, both facing toward the main portion of the machine. Overburden is removed by placing the bucket on the ground at a point distant from the machine and pulling it toward the machine, filling the bucket in the process. Once filled, the machine pivots about a central axis and the bucket emptied at a spoil pile somewhat away from the area being excavated.
Smaller draglines are crawler mounted (much like a military tank) and capable of movement in the same way, albeit at much slower speeds. However, as draglines (and their digging buckets) increased in size, crawler mounting was found to be impractical and in the early 1900's, the "walking" dragline was developed. The walking dragline is so named because it takes short "steps" and uses a "walk leg" mechanism (which resembles a human leg) to do so. A difference is that in a walking dragline, both legs step simultaneously.
To give some perspective to the following discussion, a large walking dragline--made by Harnischfeger Industries of Milwaukee, Wis., and incorporating the invention--has a main housing portion (including the machinery deck, operator's cab and the like) which is about 105 feet long, about 80 feet wide, about 40 feet high and weighs about nine million pounds. The boom extends about 300 feet and the capacity of the digging bucket is about 80 cubic yards. The walk legs of such dragline take steps about seven feet in length.
In a specific application in which the inventive groove arrangement is used, one embodiment of the bushing-type bearing described below is about nine feet in diameter and in excess of two feet in cylindrical length. An adult can easily stand upright inside the "ring" formed by the bushing! The walk legs of a walking dragline preferably use a bushing-type bearing since they are heavily loaded, the leg operates at very slow speed and may be called upon to "walk" only once or a few times per day.
An earlier bearing lubrication groove arrangement involved one or two continuously-cut grooves formed on the interior cylindrical surface of the bearing. This earlier arrangement is aptly described as resembling opposed sine waves since the paths defined by the grooves closely resemble the "trace" of two alternating voltages which are 180.degree. out of phase.
A problem with this earlier lubrication groove arrangement is that there are significant portions of the bearing surface which are not effectively lubricated and therefore, are subject to inordinate wear. Another problem is that the sine wave grooves do not satisfactorily "flush" out small wear particles nor do they provide for bearing edge lubrication.
Another earlier arrangement involved a number of individual grooves formed in the bearing surface in an axial direction, i.e., parallel to the cylinder central axis of the bearing. For reasons explained below, such axially-oriented grooves do not satisfactorily distribute grease in an axial direction. As a result, some areas of the bearing surface are "starved" of grease.
The invention is directed to an improved lubrication groove arrangement which helps maintain a film of lubricant in boundary lubricated bearings. As will become apparent, the invention resolves some of these difficulties in unique and imaginative ways.